My son had this problem. Of course kids hang on to the belief that we put them in the right classroom, and that the teacher must "know" what we are capable of and therefore they are deliberately 'dis-ing' our kids, for as long as they can. School is also a place where kids get praised, and the teacher is almost a diety at this stage - remember all that rivalry in the Bible? You liked his offering better - and kids who aren't part of the norm do get their offerings passed over for other offerings all the time.
Do not tell your kid he is gifted right now. That isn't the answer. This is one of those times in life were you have to move quietly behind the scenes and stop the teacher from giving the child baby work - because you want your child to grow in self esteem, and he can't grow unless he learns to overcome obsticals, which is current work isn't.
So my advice is to meet with the teacher in person, and come up with some work you can place in his folder so he has something reasonable to do during classtime. This can't be solved by talking, only by doing. Kids don't usually self-advocate well until age 10, and I don't think this is because of the kids themselves, just that it's too big of a jump for most adults to handle.
Smiles,
Grinity
